Spinal bone mass is low in daughters of women with postmenopausal osteoporosis, but the pathogenesis is unknown. We will test the hypothesis that low bone mass is due to diminished osteoblast-mediated new bone formation in daughters and controls on a low calcium diet and calcitrol and measure bone cell biochemical markers of osteoblasts (osteocalcin) & osteoclasts at baseline and after 6 days of treatment. The primary endpoint is the change in serum osteocalcin with diet and calcitrol.